Acid and non-acid forms of kaolinite clays were found by potentiometric and conductometric titrations to possess a weak acid species, the concentration of which was increased by acidic preparation conditions and by the presence of soil organic matter bound to the clay. A stronger acid species was also found in untreated and in organic-free, HCl-treated samples (washed free of excess acid). The end points for organic-free and/or ion-exchanged samples were used to predict the end points for untreated samples. A surface-chemical model involving MOH2+, MOH, and MO− species (where M = Al and/or Fe) was fitted to the titration data and to the cation-exchange capacities. MOH2+ is the stronger acid and MOH the weaker acid; exchange of Na+ counterions by H+ converts MO−Na+ sites to MOH sites. Humic acid was probably complexed or chelated to some hydroxylated Al/Fe sites through COOH and phenolic OH groups. The COOH groups contributed supplementary stronger acid species which were not exchangeable, whereas the OH groups contributed supplementary weaker acid species and also increased the CEC relative to that for organic-free samples.

The aspect ratios of common clay minerals have been determined from conductometric titrations. The sample set comprises 11 Na-saturated bentonites, 16 smectites with different interlayer cations, three illites/muscovites and two talc dominated specimens. It is shown that the aspect ratios of smectites saturated with divalent cations are lower than those of the same smectite saturated with a monovalent cation. This observation is discussed in terms of the number of smectite layers making up a particle.

It has been established that disagreements between different methods of particle size determination of clay minerals can be ascribed to the non-spherical shape of the clay particles. However, by having aspect ratios available, particle sizes can be harmonized. One frequently used approach to obtain aspect ratios is to compare particle sizes originating from at least two devices operating on the basis of different physical principles. In this contribution aspect ratios of nine kaolinite-dominated and one dickite-dominated sample were determined by conductometric titrations. The aspect ratios obtained were then successfully used to correlate particle size distributions from dynamic laser scattering and acoustic spectroscopy.